There have been known image forming apparatuses that perform image formation by developing electrostatic latent images formed on a photosensitive drum.
Such image forming apparatuses may include a detachable process unit in order to facilitate replenishment of toner. The process unit may include a developing cartridge and a drum cartridge. The developing cartridge accommodates a toner tank for holding toner and a mechanism for developing an image using toner. The drum cartridge accommodates a photosensitive drum (functioning as an image carrying member) and mechanisms provided around the photosensitive drum. The developing cartridge is designed to be attachable and detachable with respect to the drum cartridge.
For example, as shown in FIG. 8, a drum cartridge commonly includes a photosensitive drum 101; a charging device 102 that uniformly charges a surface of the photosensitive drum 101; a transfer roller 103 that is used to transfer, onto a sheet P, a visible image (a toner image) that is obtained by development of an electrostatic latent image formed on the photosensitive drum 101 by using toner; and a cleaner 104 that removes foreign matter (e.g., paper dust) adhering to the photosensitive drum 101 after image transfer. A housing of the drum cartridge is partially indicated in FIG. 8 by a dot and dashed line. The housing of the drum cartridge covers various portions and members except a sheet inlet 105 is provided through which a sheet P is taken into the drum cartridge, a sheet outlet 106 is provided through which the sheet P is ejected from the drum cartridge, a back of the charging device 102 may form a portion of the housing, and a laser path 107 is provided through which laser light emitted from a scanner unit passes.
A discharge-type charging device, such as a scorotron charger, generally is used as the charging device 102 to perform non-contact charging on the photosensitive drum 101. The charging device 102 is commonly disposed above the photosensitive drum 101. In this case, the cleaner 104 needs to be disposed at an upstream position from the charging device 102 with respect to a rotating direction of the photosensitive drum 101 (a clockwise direction in FIG. 8), and the charging device 102 is arranged next to the photosensitive drum 101 in a horizontal direction in conjunction with an arrangement of the other elements.
When a member, for example, a brush, used as the cleaner 104, contacts the photosensitive drum 101, the flow of air around the photosensitive drum 101 is obstructed by the cleaner 104 and an inner wall of the housing of the drum cartridge. As a result, moisture in the air and ozone generated by the charging device 102 are likely to build up at an upper portion of the cleaner 104 in the drum cartridge.
If the photosensitive drum 101 is not rotated while moisture and ozone build up inside the drum cartridge, a film developed on the surface of the photosensitive drum 101 (e.g., a buildup of foreign matter on the surface of the photosensitive drum 101) may excessively take up or include the moisture and ozone, such that it may be difficult to expose the surface of the photosensitive drum 101 with laser light. If printing is performed after the photosensitive drum 101 is left in such a condition, the photosensitive drum 101 may not be able to carry enough toner at the moistened portion on the filming, so that an undesired white stripe (a band of a print dropout that extends in a sheet width direction perpendicular to a sheet conveying direction) may appear on a printed result.
In order to resolve the above problem, for example, Japanese Laid-Open Patent Publication No. 5-216321 discloses a device that includes a duct having a fan and a pipe provided between a charging device and a cleaner in order to forcefully exhaust ozone generated by the charging device. The inclusion of this new duct element, however, undesirably increases the size of the image forming apparatus.